The present invention is directed to a method and apparatus for monitoring the relative elongation characteristics of a moving electrically conducting steel or other metallic strip in order to provide a measure of the relative length or elongation of the strip at a number of points across the strip width in order to determine the shape profile. A plurality of sensors located at spaced positions across the width of the strip measure the change in electrical capacitance between the moving strip surface and the sensor due to variations in the flatness of the strip. Electrical output signals from these sensors may then be correlated to provide a measure of the relative length or elongation, or the shape profile, of the strip at each of the sensing positions.
The present invention finds particular utility in connection with processes for manufacturing steel strip. Under some circumstances, and at certain points in the manufacturing process, an unsupported steel strip may exhibit a bowed, drooping, wavy or otherwise non-flat shape profile when viewed in end cross-section. In some cases, a significant length of the strip may be completely unusable if the distortion is extensive. In other applications, the non-uniform elongation of the strip may cause problems as the strip tracks across supporting rollers, or is wound in a coil.
It has been observed that various types of non-flat strip shape profile characteristics may occur during the manufacturing process. Typical types of profile characteristics are illustrated in FIG. 1A-FIG. 1D, where similar elements are similarly designated. In each profile representation, the left-handmost longitudinal strip edge occurring at a position 1 is designated 1a. The longitudinally extending central portion of the strip is designated position 2. The right-handmost longitudinal strip edge occurring at a position 3 is designated 3a. The normal boundaries of the flat strip are designated by the lighter construction lines a, while the actual boundaries of the strip having a particular profile are illustrated in darker lines and designated as indicated hereinafter.
For example, one possible strip shape profile is illustrated diagrammatically in FIG. 1A wherein the right-handmost edge of the strip, designated position 3, droops or sags. This may occur during the rolling operation where variations occur in the cross-sectional profile of the rolling gap. Since the edges of the strip are constrained during the rolling process, resulting transverse variations occur in the elongation of edge 3 of the strip in order to maintain constant volume. In other words, inasmuch as edge 3 is longer than edge 1 and the center 2 of the strip, the longer edge will tend to sag or droop in an unsupported length of the strip and exhibit a wavy edge as at 3c.
Another variation (generally referred to as a "tight center") is illustrated diagrammatically in FIG. 1B where the longitudinal edges 1 and 3 are longer than the center portion 2. Here it will be observed that both longitudinal edges 1c and 3c are wavy.
A similar type of condition is illustrated in FIG. 1C where the center portion 2 of the strip is elongated with respect to the longitudinal edges 1 and 3. This results, in an unsupported strip length, in a profile of curvature opposite to that illustrated in FIG. 1B. It is often common to find a wavy portion 2C (sometimes referred to as "pockets") at the center portion of the strip, with straight outer edges 1c and 3c.
Finally, another possible characteristic profile is illustrated in FIG. 1D, where the right longitudinal edge 3 is longer than center 2, which in turn is longer than the left longitudinal edge 1. This results in a condition where the entire strip droops downwardly from longitudinal edge 1C to right longitudinal edge 3C. This is to be distinguished from the condition illustrated in FIG. 1A wherein there is substantially no relative elongation between strip edge 1 and center portion 2.
It is desirable to be able to continuously monitor the shape profile characteristics of the strip in order to provide a continuous measure of the relative length or elongation at particular points in the processing line. This information, whether it reveals center buckle, long edges or wavy conditions, may be used to provide additional compensation for flattening, or heat treating steps on the processing line, or such information may be stored in a suitable memory for further analysis.